convert-nonogram

convert-nonogram is a tool that converts images to nonograms. Currently, it only outputs the widely-used XML-based webpbn format and the olsak format (with the extension .g).

convert-nonogram does an exact image-to-nonogram format conversion. If you're looking for something that will take an arbitrary image and make a solveable (black and white) nonogram out of it, you can try Walter Koster's tool.

How to use it

I use convert-nonogram to evaluate the solvability of nonograms while editing them as an image. You can install it with cargo install convert-nonogram.

All images supported by the image crate are supported as input, but if you try to create JPEG nonograms, you're going to have a bad time.

With pbnsolve

This is what I do, since pbnsolve provides useful information about difficulty. You'll have to download and install it from a tarball.

Then, to evaluate an image, do:

convert-nonogram examples/tea.png | pbnsolve -tu

(-t requests detailed difficulty output, and -u requires checking for uniqueness. You can add -aL (or -aE; I don't fully understand the difference) to stop solving when it's not possible to proceed with "line logic". You can add -b to suppress output of the solved grid, but it's useful when debugging a non-unique nonogram or partially-solvable nonogram. pbnsolve's README file documents its other flags.)

Here's a somewhat tricky nonogram that's solveable with only single-line reasoning. The "Lines processed" (relative to "Lines in puzzle", which is the sum of the width and height) is the best indicator of difficulty, I think:

$ convert-nonogram examples/shirt_and_tie.png | pbnsolve -tu
UNIQUE LINE SOLUTION:
.........aaaa..
........a....aa
....aaaaaaa...a
...aa.....aa.ab
..aa.......aabb
..a...........b
..a...a.aaaaa.b
..a...a.a...a.b
.aa..aa.aaaaa.b
.a...aa.a...a.b
.a..aaa.a...a.b
aa..a.a..aaa..b
a...a.a......bb
a...a.a......bb
aaaaa.a......bb
ab.a..a......bb
a..a..a......bb
aaaa..a.......b
......aaaaa....
..........aaaaa
Cells Solved: 300 of 300
Lines in Puzzle: 35
Lines Processed: 149 (400%)
Exhaustive Search: 0 cells in 0 passes
Backtracking: 0 probes, 0 guesses, 0 backtracks
Probe Sequences: 0
Plod cycles: 1, Sprint cycles: 0
Cache Hits: 0/0 (0.0%) Adds: 0  Flushes: 0
Processing Time: 0.000205 sec 

Here's the same nonogram with the button on the shirt sleeve removed. Now it requires backtracking to solve:

$ convert-nonogram examples/shirt_and_tie_no_button.png | pbnsolve -tu
UNIQUE SOLUTION:
.........aaaa..
........a....aa
....aaaaaaa...a
...aa.....aa.ab
..aa.......aabb
..a...........b
..a...a.aaaaa.b
..a...a.a...a.b
.aa..aa.aaaaa.b
.a...aa.a...a.b
.a..aaa.a...a.b
aa..a.a..aaa..b
a...a.a......bb
a...a.a......bb
aaaaa.a......bb
a..a..a......bb
a..a..a......bb
aaaa..a.......b
......aaaaa....
..........aaaaa
Cells Solved: 300 of 300
Lines in Puzzle: 35
Lines Processed: 1158 (3300%)
Exhaustive Search: 13 cells in 2 passes
Backtracking: 105 probes, 32 guesses, 32 backtracks
Probe Sequences: 32
  Found Contradiction: 31 (0 adj, 31 2-neigh)
  Found Solution:      1 (0 adj, 1 2-neigh)
  Choose Optimum:      0 (0 adj, 0 2-neigh)
Total probes: 105 (0 adj, 105 2-neigh)
Plod cycles: 1, Sprint cycles: 0
Cache Hits: 576/1102 (52.0%) Adds: 494  Flushes: 0
Processing Time: 0.001668 sec 

With nonogrid

nonogrid can provide a better and more comprehensive visual representation of ambiguities in non-unique nonograms. Sadly, it doesn't tell you anything about the difficulty of a nonogram.

Make sure to install nonogrid with cargo install --features=xml,web nonogrid to allow parsing the XML format (and to enable directly downloading nonograms from the web, because why not). Then, to evaluate an image, do:

convert-nonogram examples/tea.png | nonogrid

With the Olsak solver

The Olsak solver comes in a tarball and doesn't even have a makefile! (Just do gcc grid.c -o grid to build it.) It accepts a different input format. It does provide some difficulty information, but I haven't yet learned to understand it.

convert-nonogram examples/tea.png --olsak | grid -

With Nonny

Nonny is a nonogram editor that can open Olask-formatted nonograms. Its solver is a bit unsophisticated, but you can watch it work, which can give you an idea of what parts of the puzzle are easy to deal with and what parts are trickier.

convert-nonogram examples/tea.png --olsak > ~/.local/share/nonny/puzzles/tea.g

To export a puzzle from Nonny, I, uh, take a screenshot of the thumbnail in the Gimp, crop it, and resize the image with "none" as the interpolation technique. Maybe convert-nonogram ought to accept some other nonogram formats as input.